A carbon material is light in weight and excellent in chemical and thermal stability and has good thermal conductivity and electrical conductivity even though it is a non-metal material. A carbon material is light in weight and excellent in chemical and thermal stability and has good thermal conductivity and electrical conductivity even though it is a non-metal material. However, when a layer of a material other than carbon is formed on the carbon material, there is a problem in adhesion performance between the carbon material and the layer of the other material.
As a method for improving the adhesion performance, Patent Documents 1 and 2, for example, describes that, by treating a carbon substrate with halogenated chromium gas, a chromium carbide layer comprising Cr23C6 is formed on the surface, and the chromium carbide layer is coated with a metal by thermal spraying. However, this technique has the following problems. It takes a very long time to form a layer comprising Cr23C6 that can withstand the thermal spraying of a metal. Also, the treatment is complicated and troublesome; for example, it is essential to carry out the treatment in a hydrogen gas atmosphere and the treatment needs to be performed under a reduced pressure.